Add-on for a smartphone for smartphone-based photorefraction



FIG. 1 is a front perspective view of an add-on for a smartphone for smartphone-based photorefraction;

FIG. 2 is a left side view thereof;

FIG. 3 is a right side view thereof;

FIG. 4 is a rear view thereof;

FIG. 5 is a front plan view thereof;

FIG. 6 is a top view thereof;

FIG. 7 is a bottom view thereof; and,

FIG. 8 is a rear elevation perspective view thereof.

The broken lines depict portions of the smartphone in which the design is embodied that form no part of the claimed design. 

CLAIM The ornamental design for an add-on for a smartphone for smartphone-based photorefraction, as shown and described. 